The other battery, in a forward bay, is used primarily to provide backup power for critical systems including flight controls.

In flight, the batteries are charging but are not typically providing power.

On previous Boeing jets, wing anti-ice systems, cabin pressure, air conditioning and engine start were all pneumatically driven, powered by air redirected from the jet engine’s fan.

On the 787, all those systems are electrically driven so as to improve engine efficiency and fuel burn.

As a result, the Dreamliner uses four times as much electricity as the larger 777 twinjet, generating 1.45 megawatts, enough to power about 600 homes.

Even the first couple of tiers of the supply chain for these electrical systems are intricate.

Thales of France supplies the 787 power conversion system, with subcontracts to GS Yuasa of Japan for the main batteries; Securaplane Technologies of Tucson, Ariz., for the battery charger system; and Kanto Aircraft Instrument of Japan for the charge monitoring system.

Thales said all its systems have been certified by “very robust” processes.

“Thales is working very closely with Boeing in coordination with the investigative and regulatory authorities to understand the events and resolve the (battery) issue,” it said in a statement.

The aerospace systems unit of United Technologies supplies many of the rest of the 787 electrical systems, but it also subcontracts with multiple companies.

Nabtesco of Japan supplies the high-voltage power distributor. ECE Zodiac of France makes the power distribution panels.

United Technologies supplies two power control modules that plug into the ECE power panel motherboard.

Spokesman Dan Coulom said the aerospace systems unit of United Technologies completed more than 36,000 hours of testing to help develop and certify the 787 Dreamliner.

“We are confident in the integrity of our advanced technology systems,” he said. United Technologies “continues to work closely with Boeing and regulatory authorities to resolve any in-service issues.”